1. Field of the Invention
This invention relates generally to unauthorized user prevention devices, and more specifically relates to a sensor array for use in such devices. While applicable to many environments, the invention is especially applicable to an identification device and method to prevent the discharge of a firearm by anyone other than an owner and/or registered user.
2. Description of the Related Art
All too often there are tragic news reports of people who are gravely injured or killed by gunshots fired by a person who is not the owner or an authorized user of the firearm. Regardless of the specific cause, it is evident that many of these incidents could be avoided if the firearm were only fireable by the owner or other authorized user of the gun.
A number of prior art patents have been directed to technology for solving this vexing problem. U.S. Pat. No. 4,970,819 to Mayhak, for example, discloses a system for sensing the grip pattern of the hand of a potential user of a firearm and permitting the firing thereof if it senses a particular grip pattern of an authorized user which it has been programmed to recognize. The system includes grip pattern sensing means on the handgrip of the firearm, a simulated neural network memory capable of being xe2x80x9ctrainedxe2x80x9d to recognize a particular grip pattern and a microprocessor for accessing the neural network to inquire whether it recognizes the grip pattern being sensed by the sensing means. The microprocessor also controls means for permitting and preventing actuation of the firing mechanism of the firearm to allow the firearm to be discharged only when the grip pattern sensed by the sensing means is that of the authorized user which the simulated neural network memory has been programmed to recognize.
U.S. Pat. No. 5,603,179 discloses a safety mechanism for a firearm consisting of a specialized scanning mechanism built into the firearm""s trigger. The scanner is programmed to read the unique fingerprints of a given individual. The device is also capable of holding the programmed print information for more than one person, so that multiple people would he able to use the firearm. However, usage is limited to only those persons whose handprints have been prestored in the scanner. The scanner mechanism is connected to the firearm""s safety lock. The safety is prevented from being released without proper authorization from the scanner. When a person grips the weapon and places his finger on the trigger, the pressure of the finger on the trigger activates the scanner, and the scanner reads the fingerprint to determine if the scanned fingerprint matches one of the pre-stored fingerprint images. If the individual is an authorized user, the scanner transmits a signal to the safety, releasing this device and activating the firearm for use.
U.S. Pat. No. 5,316,479 to Wong discloses a firearm training system, which allows the measurement and display as a function of time of the hand grip force pattern applied to the grip of a firearm by a weapon hand of a shooter. This permits the detection of variations in the individual handgrip forces in the pattern during firing of the weapon. This firearm training system preferably also provides for the detection and display as a function of time of the position of the firearm trigger. The system includes separate force transducers for the side and front-to-back grip forces applied to the side surfaces and one of the front and back surfaces of the grip respectively as well as a trigger position sensor. A relative value of the hand grip forces detected by the transducers and a relative trigger position detected by the sensor are graphically displayed by the system as a function of time.
In U.S. Pat. No. 6,563,940, assigned to the assignee of the present invention, a further weapon discharge protection system is disclosed that prohibits a firearm, such as a handgun, from being fired by anyone other than its owner or other authorized person. The present invention can be considered as an improvement on the invention of U.S. Pat. No. 6,563,940 patent, and the entire disclosure of such patent is hereby incorporated by reference. In one embodiment of this prior patent, pressure sensors are arranged within the handgrip of the firearm. When one attempts to fire the firearm, he or she exerts a unique pressure signature profile on the handgrip. That is, each person exerts a pressure signature profile that is comprised of (1) the position of the hand on the gun handle; (2) pressure as a function of position on the gun handle; and (3) pressure as a function of time. Pressure signature profiles are sufficiently distinctive as a means for differentiating the owner or other authorized person, whose pressure signature profile is stored in memory, from the remainder of the population-at-large. This signature profile is most differentiating during the half of a second just prior to the trigger pull, as the user prepares to fire the weapon. Initial data show that no more than 1% of the population-at-large possess a given pressure profile. In other words, there is a very low probability that a person who is not the owner or authorized user of a gun would be permitted to fire the gun because he or she matched the stored pressure signature profile.
In one embodiment of the U.S. Pat. No. 6,563,940 patent, quartz crystals, arranged along the surface of the handle, are used as the pressure sensors. When biased these crystals, which are used in timepieces, oscillate at a fixed frequency, and pressure applied to the crystals result in repeatable, precise changes in this oscillation frequency. The electrical signals from the quartz crystals, which correspond to the pressure signature profile, or other sensor material, is inputted to a processing unit, such as a microprocessor. The signal could be the electrical signal generated by the pressure signature profile of the lawful owner or user, inputted to the processing unit for the first time. In this case, by entering a sequence of commands, the signal will be stored within the processing unit as the pressure signature profile of the owner or authorized user. On the other hand, the signal generated by the pressure signature profile could be that of a person who is attempting to fire the firearm, in which case the electrical signal outputted from the crystals to the processing unit is compared to the signal stored as pressure signature profile of the owner or authorized user. If the signal matches the signal stored as the pressure signal profile, then the processing unit activates a mechanism that allows the owner or authorized user to fire the firearm. If the signal outputted from the crystals does not match the signal stored on the pressure signal profile, then the processing unit does not activate the mechanism, so that the firearm cannot be fired.
FIG. 1 herein is taken from the U.S. Pat. No. 6,563,940 patent and is a prior art depiction of a firearm 100, which in this particular example is a handgun having a revolver design. The firearm 100 is provided with a handgrip 120 and is fired when firing mechanism 130 is actuated. The firing mechanism 130 includes trigger 140, which is pivotally mounted in the frame of the gun at 150. Movement of the trigger 140 will cause a hammer 160 to be cocked and released, thus firing a bullet (not shown) stored in the cylinder 170. The firearm 100 is provided with a safety, which is moved in and out of position to prevent and permit the actuation of the firing mechanism 130. The safety is a sliding latch member 180 adapted to engage a portion 190 on trigger 140, which extends under the latch member 180. Latch member 180 is biased by a spring 185 to a position in which it is it is adjacent to portion 190, thereby preventing trigger 140 from being pulled, in which case it pivots around pivot 150 into the fired position. In effect, latch member 180 prevents actuation of the firing mechanism. This handgun is further provided with a solenoid 195 into which an end of latch member 180 is placed. When energized, solenoid 195 retracts latch member 180, overcoming biasing force of spring 185, which removes the latch member 180 from the path of portion 190. With latch member 180 out of the path of portion 190, the trigger can be pulled, actuating the firing mechanism to discharge the firearm. The retraction of the solenoid, or any type of interlock system, is dependent upon recognition of the users as being authorized to use the weapon.
FIG. 2 is a further prior art showing, being FIG. 2 in the same U.S. Pat. No. 6,563,940 patent. The Figure is a schematic block diagram illustrating how the unauthorized user device of the patent can operate. Sensor array 125, which is arranged in the handle of the weapon and may also be arranged in the trigger, or can be part of a special retrofit grip for weapons made prior to the patented invention, provides feedback information regarding the position, pressure, and duration of a person gripping the handle of the weapon. The term xe2x80x9chandgripxe2x80x9d is defined as the grip applied to the handle of a device (presumably but not necessarily limited to a weapon) that may also include the pressure asserted on the trigger as well as the pressure asserted on the handle of the weapon. The output from the sensors is provided to comparator 210, which compares these values with values previously stored in storage member 215.
When the comparator 210 finds a match (according to a predetermined variation either built into the device or chosen by user according to a sensitivity switch (not shown)) of the output with a value in storage, the comparator indicates this match to the control unit 220. The indication that there is a match could be, for example, a logic 1 or a logic 0 that is received by the control unit. In turn, the control unit will signal release interlock 230 so that the weapon can be fired. In the case of the example illustrated in FIG. 1, the control unit/cpu 220 would energize the solenoid 195 and retract the latch member 180. It is possible that the control unit (which may or may not be separate from the cpu) could be programmed to have a limited sequence in which the weapon could be used, and once that time has passed, the control unit would again lock the interlock 230 and prevent the firing of the weapon.
The control unit/cpu 220 processes the electrical signals to develop a pressure signal profile including: (1) hand position of the user""s handgrip on the particular device as indicated by a change in pressure on the sensor array/pressure sensors; and (2) pressure as a function of position on the gun handle; and (3) pressure as a function of time.
With regard to the three items disclosed above to develop a pressure signal profile, items 1 and 2 provide information regarding the area over which pressure is exerted by a given person, i.e.xe2x80x94the outline of the hand, the outline of the fingers (item 1) pressure on the handgrip, as manifested by the position of the hand on the handgrip, and any variances in the pressure applied by over the area (item 2). Item 3 shows pressure as a function of time, which is also critical because the duration that each person applies pressure by squeezing the grip varies greatly. The pressure signature profile can enable a user to wear thin gloves and still be recognized as the authorized user, which would not be possible in fingerprint recognition systems of the earlier prior art.
Together, the three elements of the profile (items 1-3) in said U.S. Pat. No. 6,563,940 patent provide a unique pressure signal profile that no more than 1% of the population-at-large would possess. The sensors, including the piezoelectrics described above, produce a continuous analog output signal that varies in repeatable manner with applied load, and has a unique output for each level of applied pressure. The xe2x80x9cpressure signature profilexe2x80x9d is a composite signal that includes voltage changes, oscillation frequency changes, and frequency composition changes. The identification of an individual is performed using a statistical classifier that includes a set of computed weights and thresholds which separate the xe2x80x9cpressure signaturexe2x80x9d of an individual from that of the rest of the population.
When a force is applied to the handgrip the sensors output an electrical signal to the control unit. In one embodiment the control unit may be a microprocessor located within the firearm, for example, within the handgrip. The control unit compares it to the signal stored as the pressure profile of the lawful owner or authorized user. The microprocessor simultaneously reads the signals from all of the sensors and continuously searches for the dynamic pattern corresponding to the valid xe2x80x9cpressure signature.xe2x80x9d Components of the sensor signal are multiplied by the computed weights and stored thresholds are applied. If the signal exceeds these computed thresholds then the firearm is allowed to fire during a predetermined time interval (e.g. 500 milliseconds).
Once the pressure signal profile has been identified as that of an authorized user, the decision as to how long such an authorized user would be allowed to use the device could be based on a number of factors that could be programmable according to an individual""s preference. For example, police officers sometimes pull weapons at armed perpetrators and order them to freeze. Sometimes there can be a xe2x80x9cstandoffxe2x80x9d where the police have a weapon pointed at a particular perpetrator, who is not putting down his weapon nor has his hands in the air, prior to being handcuffed. If the time permitted to fire the weapon is too short, the gun could reset and the police officers would be unable to defend against a subsequent attack by the perpetrator (or possible accomplices) until the gun was gripped again, or reactivated by pressing an xe2x80x9conxe2x80x9d switch, etc. If the time is set for too long, the weapon could be wrestled from the authorized user and fired by an unauthorized user.
A Motion sensor could also be included both to begin the process by activating the device, and after a certain period of time without any motion, to end it. Since a firearm is typically pointed down while in a holster, a predetermined tilt angle could be programmed in to activate the detection, or the mere squeezing of the grip while induce a voltage in the piezoelectric type sensors that could turn on the device.
Suitable sensors in this prior art disclosure include a sensing element into which a piezoelectric element has been embedded. Suitable piezoelectric elements include quartz crystals. Other suitable piezoelectric materials including lead titinate and lead zirconate, could be used in either a crystalline or film form. The pressure signal could also be measured using strain gauges or micro-machined pressure sensors (MEMS).
Systems employing piezoelectric materials, such as the crystals described above, produce an electrical output when they experience a change in load, i.e., pressure. Making use of this phenomenon, an embodiment of the U.S. Pat. No. 6,536,940 patent includes the transmission of electrical signal from the sensors, in response to pressure applied when a person grips the handle of the firearm, to a control unit located within the firearm. A purpose-built electronic circuit is used to convert the voltage and frequency changes measured from the sensors into a digital signal read by the processor. An electrostrictive system could also be employed.
This xe2x80x9cpressure signaturexe2x80x9d signal is programmed into the handgun by an independent station that is held by the authority that registers handguns. Such authority, for example, could be a state or local entity, or even an authorized third party. The owner of the handgun fires the gun ten to twenty times, and the pressure patterns unique to that individual are computed by a purposely-built data acquisition and analysis system. It is protected from abuse by one of several possible mechanisms, including encryption of the stored signal and tamper detection systems that can completely disable the firearm.
Grip pattern signals from sensing means 125 are fed from the firearm 100 over a line 129 to the host computer. A jack 131 in the butt of firearm handgrip 120 permits line 129 to be connected to the firearm. The pressure sensors and central processing unit/control unit within the handgun are powered by a power source, typically a battery system (not shown) that could be located in the ammunition clip of the handgun. This arrangement allows the battery to be recharged in empty ammunition clips that are not in use.
The invention of the U.S. Pat. No. 6,563,940 patent is also applicable to devices other than fire arms. A Steering wheel of a vehicle may e.g., either have sensors built in, or a steering wheel cover could be attached over the steering wheel. The unauthorized user prevention device could be located anywhere in the automobile, for example, in the steering column, under the dashboard, under the hood, in the trunk, etc. The device could be powered by the vehicle""s battery. Similar to the pressure profile used for preventing unauthorized users from activating a weapon, a pressure profile from squeezing the steering wheel based on the three items (position, pressure and time) can be stored. There can be an ignition cutoff switch, fuel cutoff switch, etc. that would only be deactivated when the user squeezing the steering wheel matches a profile in storage, thus being an authorized user. The user could squeeze the wheel with a xe2x80x9csecret handshakexe2x80x9d (which can also be used with a weapon) that could be anywhere from just one finger to all ten. The number of possibilities, based on in part on the number of sensors and the number of combinations of fingers squeezing different areas at different pressure for different time periods would result in the chance of an unauthorized user gaining access as extremely remote being one in thousands or tens of thousands, as opposed to one in one hundred. A control unit or cpu would compare the profiles and deactivate the interlock.
The unauthorized user prevention device of U.S. Pat. No. 6,563,940 could also work on a xe2x80x9ckeylessxe2x80x9d door handle. A series of sensors could be embedded in the door handle. The user gripping the door would create a pressure profile based on position, pressure and time. This profile could be compared with stored pressure profiles that would release the lock if the person gripping the door handle matches one of the profiles in storage. The cpu or control unit could be remotely located, and the sensor feedback could be transmitted to the control unit by wire, fiber optics, or RF.
The biometric pattern recognition technology discussed in the foregoing prior art uses electrical signals provided by miniature pressure sensors typically located by embedding in the gun handle. The authentication algorithm performance depends on the density, size, shape, and location of pressure sensors on the handle of the handgun. Fabrication of pressure sensor arrays embedded in the gun""s grip using discrete piezoelectric elements (quartz, PZT ceramic, or lithium niobate) has proven inefficient and costly because of the complex ergonomic shape of the gun grip. The discrete pressure sensors are solid plates. The gun grip has to be mechanically machined in order to install the pressure sensors and ensure good mechanical contact with the palm of the gun user. The fabrication of such a gun grip is highly inefficient, expensive, and unreliable. The sensors are vulnerable to damages caused by extensive pressure or exposure to moisture. Fabrication difficulties limit the number of sensors that can be installed in the grip (typically a maximum of around 10). Low sensor density in the pressure array decreases the resolution, which depends on the number of xe2x80x9cpressure pixelsxe2x80x9d. Other serious limitation of the embedded piezoelectric sensors include the strong dependence of the piezoelectric effect on temperature. Temperature variations of xc2x125xc2x0 C. can cause significant changes of the frequency of the quartz resonators. Lithium niobate is even more sensitive than quartz to temperature changes. PZT ceramics depolarizes irreversibly at 90xc2x0 C.
Now in accordance with the present invention, improvements in the sensor array are provided for use in a module for preventing unauthorized use of a firearm or other device. The module to which the invention is applicable can be of the type in the U.S. Pat. No. 6,563,940 patent, i.e., including a plurality of pressure sensors for sensing a user""s handgrip on the gripping surface of the device; comparator means for comparing a pressure signature profile compiled from an output from said pressure sensors with at least one pressure signature profile in storage; and means for preventing operation of the device when the compared profiles do not match. The improved sensor array comprises a first set of spaced electrically conductive lines formed on the gripping surface; a thin layer of (preferably) piezoresistive material formed overlying the first set of conductive lines; and a second set of spaced electrically conductive lines formed over the piezoresistive layer. The lines of the second set are orthogonal to the lines of the first set, to establish a grid-like pattern of conductive lines sandwiching the piezoresistive layer. The projected intersections between the lines of the first and second sets (i.e., the grid crossing points) thereby define with the intervening portion of the piezoresistive layer, an array of sensors which are responsive to pressure applied against the gripping surface by a user of the device. Such pressure changes the electrical conductivity in the path including the intersecting lines and intervening piezoresistive material. Signal outputs from the electrical paths including the array of sensors serve to define the pressure signal profile.